The use of cable ties to bundle or secure a group of articles is well known. Known cable ties of conventional construction are elongate members having a head at one end, a tail at the other end, and a longitudinal strap therebetween. The strap is wrapped around a bundle of articles and the tail is inserted through an aperture or passageway in the head. The head of the cable tie typically includes a locking element which is engagable with the strap so that when the tail is pulled through the passageway in the head, the locking element secures the strap in the head.
The locking element may be formed as a fixed member which interferes with the strap being inserted through the passageway in the head, or may be formed to deflect away from the strap during insertion therepast. Fixed locking elements require relatively high insertion forces in order to insert the strap through the passageway in the head as such locking elements require elastic deformation of one or both of the locking element and strap for strap insertion. U.K. Patent No. 2 163 707 provides an example of a cable tie having a fixed locking element within the passageway of the head which requires mechanical elastic deformation in order for the strap to be inserted past the locking element. U.K. Patent Application No. 2 024 918 provides another example of a cable tie having a number of fixed locking elements within the passageway in the head which interfere with strap insertion and require elastic deformation to allow the strap therepast. From an ergonomic perspective, such cable ties may generally require unacceptably high insertion forces due to the locking element interfering with the insertion of the strap.
Deflectable locking elements, conversely, are well-known in the art for reducing the force required for strap insertion through the passageway. Deflectable locking elements are designed to acquiesce to the strap during strap insertion while being biased into engaging the strap during attempted withdrawal of the strap in a direction opposite to the insertion direction. Cable ties including a deflectable locking element generally take the form of a so-called one-piece cable tie, which include an integrally-formed flexibly mounted pawl, or a two-piece cable tie, which include a metallic locking barb embedded into the cable tie head so as to protrude into the passageway. U.S. Pat. No. 3,965,538 discloses a one-piece cable tie where the locking element is formed integrally within the head of the cable tie. Such cable ties require relatively low insertion forces but provide relatively lower long-term loop tensile strength. U.S. Pat. No. 5,517,727 discloses a two-piece cable tie which employs a metal barb embedded in the head at an acute angle to the inserted tail. The metal barb bites into the strap upon any attempt to withdraw the strap therefrom. Two-piece cable ties generally require a relatively higher insertion force but provide a relatively higher long-term loop tensile strength.
The art has also seen hybrid-type cable ties which include both fixed and deflectable locking members within the head. French Patent Publication No. 2 502 265 discloses a one-piece parallel-entry cable tie having two transverse locking teeth formed within the cable tie head which project into the passageway and engage the mating transverse locking teeth formed on the strap. One of the locking teeth in the head is formed on a deflectable pawl while the other locking tooth is formed thereadjacent on a cross-piece from which the deflectable pawl projects and thereby remains within the passageway throughout strap insertion. European Patent Application No. 0 090 726 discloses a one-piece parallel-entry cable tie which provides a pair of tapering or triangular detents on the sidewalls of the passageway for frictionally engaging the longitudinal edges of the strap. The tapering design of these detents tends to force the strap away from the cross-piece which supports a deflectable pawl while frictionally gripping the longitudinal edges of the strap. Each of these cable tie having a hybrid design therefore provides fixed locking members which project into the passageway and frictionally engage the full length of the strap being inserted therepast, further increasing the insertion force required for strap insertion.
Thus while the hybrid designs of the prior art employ fixed teeth on the cable tie head, these teeth increase the insertion force required throughout strap insertion through the head because, in order to provide any locking capability at all, these fixed teeth must protrude into passageway and frictionally engage, and thereby impede, the entire portion of the strap being inserted therepast.
As noted above, one-piece cable ties provide a flexibly mounted pawl that is deflected by the strap during strap insertion through the passageway in the head. Both the pawl and the surface of the strap which the pawl engages typically include transverse locking teeth which interact when the forces applied to the strap attempt to withdraw the strap back out of the head. Upon application of such withdrawal forces, the transverse locking teeth on the pawl engage the transverse locking teeth on the strap to prevent the strap from being withdrawn from the head in a direction opposite to the insertion direction.
However, when insertion forces are applied to the tail of the cable tie, or to that portion of the strap which has been inserted through the head and now protrudes from the passageway, the strap will stretch to a certain extent. Stretching of the strap thereby causes the transverse locking teeth on the strap to be spaced further apart so that their interaction with the unstretched transverse locking teeth on the pawl may be adversely affected. The withdrawal forces acting on the strap would be transferred to less of thc transverse locking teeth on the pawl as the pitch alignment of the teeth on the strap has been disturbed. There is a higher likelihood of the pawl failing to retain the strap or to prevent slippage of strap in the withdrawal direction, thereby resulting in a less secure bundling.
The art has also seen cable ties, such as that disclosed in U.S. Pat. No. 3,886,630, which provide a passageway through the head in a direction substantially parallel to the strap. These so-called parallel-entry cable ties may generally have a lower profile, in that the cable tie head does not protrude as far above the articles being bundled, than the more conventional orthogonal-entry cable ties in which the passageway extends through the head in a direction substantially transverse to the plane of the strap. U.S. Pat. No. 3,965,538 provides an example of a parallel-entry cable tie. A lower profile is especially desirable in instances, such as with long lengths of bundled aircraft cable being pulled through bulkhead openings or across edges or corners in a crawlspace, where the cable tie head could catch on a projection and be pulled relative to the bundled articles.
The ability of a cable to resist being pulled relative to the bundled articles is also related to the strap being able to tightly encircle the bundled articles. The smaller the bundling radius that the strap is able to assume, the smaller the diameter of a bundle that the cable tie may secure. When a cable tie bundles a number of articles presenting a bundle diameter that is greater than the bundling radius of the cable tie, the cable tie will be better able to secure that number of articles and thereby minimize slippage of the cable tie along the length of the bundled articles.
Some parallel-entry cable ties, such those disclosed in U.S. Pat. Nos. 4,272,047 and 4,631,782, position a flexible pawl within the head so that the passageway is between the pawl and the articles to be bundled. When the cable tie is assembled, the pawl is accessible and may be disengaged from the inserted strap. Such cable ties are therefore not tamper-resistant as the pawl will be accessible and the bundle of articles may be released from the cable tie.
It is also known in the art to provide tools which perform the functions of pulling the tail and strap through the head. Some tools also include the capability of cutting-off a portion of the tail and strap which exits out from the passageway in the head. Such tools, however, result in exposed sharp edges at the truncated end of the strap exiting the head. The sharp edges on the truncated end of the strap pose a hazard to those handling the bundled articles.
It is therefore desirable to provide a low profile parallel-entry cable tie providing relatively low insertion forces and which can overcome the above-noted deficiencies in the prior art.